The very reason why I haven't bought a 7.5 Performance
Hi - I've done 14k in my 18 PP now, and I do 2 hours a day on average in it. I can confirm it cruises nice and quietly if that's what you want, and as someone said already, it's quieter in Eco mode than in Normal or Sport.
Doesn't sound at all 'boy-racer' when cruising if that's your concern. I'm 51 so my br days are long gone